The present invention relates to disk file systems and more particularly, the invention relates to the positioning control of one or more transducers relative to the recording surface or surfaces of and in such a disk file system.
Disk file systems form an important portion in computer systems, terminals, minicomputers, or the like. As a whole, they constitute memory extensions and input and output equipment for the main frame of such a facility. Usually, the disk file system includes at least one disk with a magnetic coating on one or both sides, and if the system is of the movable arm variety, a transducer or transducer assembly can be positioned in selected radial distances from the center of rotation of the disk surface. The transducer as so positioned cooperates and electromagnetically interacts with a particular track, also called a cylinder if the particular system includes plural disks or disk packs. Moving the transducer with its arm into alignment with a different track requires usually rapid actuation and movement of the transducer carrier in radial direction to or from the center of rotation. This operation is commonly referred to as a seek operation.
A disk file usually includes a command unit or controller and one or more disk drives, each having a single linear motor for moving the transducer or transducer assembly connected to the command of control unit which, in turn, interfaces with the computer or other digital equipment facility for receiving and accepting data for the purpose of disk file storage. Data retrieved from a disk drive pass also through the control or command unit, usually for storage in a random access storage device of the computer, terminal, etc.
In addition, the control or command unit will receive control commands for purposes of initiating the necessary accessing operation to a particular cylinder in a disk drive. The control or command unit, on the other hand, provides for the particular control of one or more of such disk drives, including control and initiation of any necessary seek operation.
In order to move the or a transducer to a different position pursuant to such a seek operation, the control and command unit will issue particular signals to be used in and by a control circuit for the linear motor in order to move the transducer or transducer assembly from one particular position to another particular position. It is, of course, apparent that these positions are very accurately defined and the motion must be carried out with an accuracy commensurate with the track spacing and width. Moreover, subsequently to such a seek operation, it is necessary to retain the transducer or transducers in centered positions above the respective track.
The motor driving the carriage is usually controlled in several different feedback operations. During a seek a speed command signal is formed from pulses (called step pulses) furnished by the command unit and representing the number of tracks across which the carriage transducer is to be moved. The carriage, in turn, signals back pulses (called detent pulses) representing the tracks across which the transducer actually moves. The speed command signal is formed from a difference in counts of the step and detent pulses. Another feedback signal is a speed signal of the carriage to be compared with the speed command signal as generated to stabilize movement of the carriage into the desired position. The third feedback is used to position the carriage in a centering position as far as the transducer-track relation is concerned; a position feedback is generated for that purpose, involving a grating on the carriage and a stationary pickup. The recurring pattern of the grating is used to generate the detent pulses and portions of the gratings are used to generate the position feedback signal.